The long-term objective of this project is to optimize benefit from a cochlear implant for individual patients. Recent research has shown the importance of individualized selection of speech coding strategy, stimulation rate, and minimum and maximum stimulation levels on each electrode in the speech processor map to optimize speech recognition and preference in everyday life. Further research is needed to determine the efficacy of new input and output speech processing for individualized fitting. Although electrical compound action potential thresholds (obtained with Neural Response Telemetry [NRT]) combined with behavioral responses have proved valuable for selecting map minimum and maximum levels on each electrode, it is unknown how NRT amplitude growth, refractory recovery, and cross-channel forward masking functions can be used to select map parameters best matched to an individual's electrical hearing. There is an urgent clinical need to determine how these NRT/NRI (Neural Response imaging) measures can be combined with behavioral measures in the fitting of implant parameters to optimize speech recognition more efficiently and effectively in adults and children. For the proposed research, electrical stimulation has been divided into two domains: input signal processing and output signal processing. Specific Aim 1 evaluates effects of changing processing of the input signal to the speech processor on speech recognition and preference in everyday life (e.g., emphasizing transient speech sounds, criteria for assigning frequency boundaries to electrodes). Specific Aim 2 evaluates effects of changing processing of the output signal on speech recognition and preference in everyday life (e.g., sequential stimulation of all electrodes vs roving stimulation of selected electrodes each cycle, effect of pulse duration and monopolar vs tripolar stimulation on electrodes). Specific Aim 3 evaluates use of NRT/NRI and behavioral measures for individualized fitting of implant parameters in adults and children. Specific Aim 4 evaluates the effect of various factors (e.g., position of electrodes in the cochlea, response to NRT/NRI measures, cognitive function, verbal abilities, etiology, and biographical factors) on word recognition in adults. Outcome of this research holds promise for marked improvement in clinical care of cochlear implant recipients.